The Coma cluster is the ideal place to study galaxy structure as a function of environmental density in order to constrain theories of galaxy formation and evolution. Here we present the spectroscopy of 35 early type Coma galaxies, which shows that the age spread of early type galaxies in the Coma cluster is large (15 Gyrs). In contrast to the field, the dominant stellar population in all (massive) Coma Es is older than 8 Gyr, while only S0s, which possess extended disks, can be as young as 2 Gyr. The old, most massive Es show a strong light element enhancement, probably due to a rather short star formation time scale and hence to a SNII -- dominated element enrichment. The lower mass S0s are much less enhanced in light elements, indicating a longer star formation time scale. The measured absorption line index gradients support the idea that early type galaxies formed in processes that include both stellar merging and gaseous dissipation.
تحميل البحث